Telephone is one of the most widely used communication equipments in the world. At first, it was merely a convenient tool to allow people to communicate while they are physically separated. Recently, many new products and services use telephone network as communication medium. Examples are electronic mails, videophone, the World Wide Web, etc. However, many users found out the performance of these products and services are below acceptable level. The main reason for the poor performance is that a large amount of data needs to be delivered from one point to another. Thus, the performance of all these products and services will improve with increasing bandwidth.
An example of the need for bandwidth is the development of teleconference devices that can communicate using regular telephone lines. Many companies have tried to developed videoconferencing products (such as videophones) since 1964. There are three major hurdles in the product development: cost, quality, and connectivity. A successful videoconferencing product must overcome these three hurdles. Currently, most homes are connected with regular phone lines, known in the industry as the Plain-Old-Telephone-System (POTS). The low bandwidth of POTS has been a great road block which keeps vendors from offering an acceptable videoconferencing product to the consumer market.
There were suggestions to use high bandwidth communication channels, such as Integrated Services Digital Network (ISDN) lines, to carry videophone communications. ISDN line has a bandwidth of 64 kilo-bits per second (Kbps), corresponding to a 1B channel, up to 384 Kbps, corresponding to a 6B channel. Most business videoconferencing products are based on ISDN because of the availability of the needed bandwidth. Unfortunately, ISDN is relatively expensive and is less popular than POTS in practically everywhere in the world. Still, many large corporations can justify installing ISDN-based videoconferencing products because they can save travel expenses and encourage business communications. However, conventional business videoconferencing products are not popular among small businesses, and are definitely unlikely to be justifiable for general public.
There are predictions that ISDN lines will become popular in the future. It is known that POTS takes decades to reach today's wide-spread usage, both domestically and internationally. Assuming that the growth of ISDN follows the historic growth path of POTS, it may take another 30 years before most household are connected to ISDN lines. Thus, it is unlikely that ISDN-based videophones will become popular in the near future.
There are other developing technologies, such as Asymmetric Digital Subscriber Line (ADSL), high bit-rate DSL (HDSL), very high bit-rate DSL (VDSL), Hybrid Fiber Coax (HFC), and Community Antenna Television (CATV). These technologies promise high bandwidth, typically higher than 1 Megabits per second or 1 Gigabits per second. However, they are either not bi-directional, not callable or not widely used.
Based on the above considerations, POTS is the best medium in the foreseeable future in terms of cost and connectivity. The worldwide infrastructure of POTS is mostly complete. Cost is low. The only hurdle is the bandwidth. Thus, it is desirable to develop ways to improve the bandwidth of POTS.
Various modulation schemes have been developed to improve the bandwidth of POTS. An example is the V.34 standard, which allows one single POTS line to communicate at 28.8 Kbps (or in some cases up to 33.6 Kbps). Looking at the technology advancements from the past, it is on the safe side to forecast that eventually faster MODEM modulation schemes over POTS will be introduced and standardized. However, it is recognized that there is a limit as to how fast data can travel along a POTS line.
Another example of the need for higher bandwidth is the Internet. During the past few years, many homes have been connected to the Internet. A typical user of Internet is attracted to beautiful multimedia images offered by the World Wide Web (the Web). However, it is found that retrieving these images over the Web is very slow because of the large data size and low bandwidth of POTS.
It can be seen from the above that it is desirable to increase the bandwidth of telephone communication with minimum cost and inconvenience to users.